Fuel delivery question

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by Drewfrazier, Jul 27, 2020.

  1. Drewfrazier

    Drewfrazier Registered Member Premium Member

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    My 72 350 sat in the garage for three weeks while we were out of town and when I returned, the fuel filter glass was full, but only with air. No fuel getting to the carb so that bad boy is not starting. Not even the whiff of unburned gas after cranking it for a couple minutes (15 seconds at a time). Can someone give me a quick tutorial on how to wake up a fuel pump that has been working great but resents neglect? Which circuit is it on the fuse box, for starters? Thanks, guys!
     
  2. bp71k5

    bp71k5 3/4 ton status Premium Member

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    is this the original 350 with a mechanical pump? I’m assuming not if you are asking about the fuse box. ;)
     
  3. Drewfrazier

    Drewfrazier Registered Member Premium Member

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    It is the original small block. The fuse box was only a guess On my part. Leaving the ignition on did nothing to fill the fuel line. The other clue was there was no smell of gas in the air the way there usually is.
     
  4. Shawn

    Shawn Nuckin Futz! Premium Member GMOTM Winner Author

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    If no fuel, then time for new mechanical pump. Many people upgrade to electric but there's no difference in performance. Electric will be easier to start when left over time.
     
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  5. Wes Harden

    Wes Harden 1/2 ton status Premium Member

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    First is there fuel in tank? Gas evaporates, esp on old cars with vented tanks.
    2 check fuel delivery hose from tank to pump, if cracked the pump will suck air.
    You could spray a small amount of starting fluid in carburetor, the engine should start and run. If the fuel delivery system is in good shape the pump should pick up fuel. Might need to do this a couple times.
    Let us know what you find.
    The above assumes mechanical pump. lower passenger side of engine.
     
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  6. bp71k5

    bp71k5 3/4 ton status Premium Member

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    ah, then you have a mechanical pump. The pump only operates when the engine is turning over. So that’s why you couldnt hear anything or the fuel filter wasn’t filling. You might try turning it over a few more and pump the gas pedal down a few times while doing it. Also make sure there’s gas in the tank of course.
     
  7. Shawn

    Shawn Nuckin Futz! Premium Member GMOTM Winner Author

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    Yeah sorry I thought you were mechanical. If you don't hear the electric pump running then you will need to check for voltage at the pump. If you volts there and no fuel coming out of the line, then definitely time for a new pump. 12v test probe works great for testing voltage at the pump. Just poke it through the wire on the positive side and see if it has any juice with the key on. If not, then its in your electrical. Could be a bad relay somwhere.
     
  8. Drewfrazier

    Drewfrazier Registered Member Premium Member

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    The starting fluid worked. I rolled the truck into the sun, noticed a tiny flow starting into the filter glass as the gas expanded, sprayed some ether into the carb and second try, it fired fine, filter glass full. Thanks so much! Great intro into fuel delivery. Who knew the camshaft did anything other than valves? I know, everyone else here...
     
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  9. Wes Harden

    Wes Harden 1/2 ton status Premium Member

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    I don't care for those serviceable glass filters. The glass may break,or end come loose, very bad. The screen filter medium is to coarse allows some dirt through.

    I prefer plastic or metal can, with paper element. placement before the pump away from heat.

    just a fyi no jugdement
     
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  10. Weird Beard

    Weird Beard Registered Member Premium Member

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    Got a free J**p Commando from a cust once that had the screw type see through filter. Caught fire at a gas station. Danger Will Robinson.
     
  11. diesel4me

    diesel4me 1 ton status Premium Member

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    I've had one of those crack when some water in the gas froze during a sudden cold snap on one truck I had,lucky it was on a straight six and the fuel line was not located on the exhaust manifold side or close enough to the plug wires to ignite the gas that dumped when the glass cracked..

    I had started the truck cold and drove off after letting it run a minute or so--I smelled raw gas BAD,then the engine started lurching,I thought I had the hand choke closed too much,but after it stalled and didn't fire right back up again I got out and opened the hood,and the gas was dripping BAD from the hood insulation,the gas squirted right into the mat!..I shut it off as fast as I could!..the glass cracked right in half on the filter...was glad I had a few universal metal filters on hand..
     

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